Landslide Hazard Zonation of Babolrood Watershed, Iran

Landslides are among the most costly and damaging natural hazards in mountainous regions of Babolrood watershed area. The main causes for the development of the landslides in the area are the influence of earthquakes and rainfall. Landslide Hazard Zonation (LHZ) maps were drawn to evaluate the potential of instability in the region. Although the region faces high potential of landslide occurrence, due to rough geomorphological characteristics and high density of forest cover, the available information is very limited. Therefore, essential spatial database of landslides is established using GIS techniques. Various data layers namely lithology, fault buffer zones, earthquake induced acceleration, drainage layout, slope degree and orientation, rainfall intensity and landuse were considered as main affecting factors. The weighting-rating system based on the relative importance of various causative factors is derived from remotely sensed data and other thematic maps. Field observation and data collection on landslides are employed to evaluate and validate landslide hazard zonation map. According to analyzed data based on five different methods, it is interpreted that a combination of lithology and fault buffer zones is the most influencing factor on the disturbance of landslide in the region. Due to high annual precipitation (over 1800 mm) and sensitivity of clay minerals to absorb water, most of the landslides occurred in the rock units that contain clay minerals. Therefore, marlstone formations of Late Tertiary period demonstrate over 35% of the landslides developed in, the region. The LHZ map is employed to evaluate potential damage to infrastructures specifically the life-line system and future development of the region.